A general class of zero-or-one inflated beta regression models

This paper proposes a general class of regression models for continuous proportions when the data contain zeros or ones. The proposed class of models assumes that the response variable has a mixed continuous-discrete distribution with probability mass at zero or one. The beta distribution is used to describe the continuous component of the model, since its density has a wide range of different shapes depending on the values of the two parameters that index the distribution. We use a suitable parameterization of the beta law in terms of its mean and a precision parameter. The parameters of the mixture distribution are modeled as functions of regression parameters. We provide inference, diagnostic, and model selection tools for this class of models. A practical application that employs real data is presented.Comment: 21 pages, 3 figures, 5 tables. Computational Statistics and Data Analysis, 17 October 2011, ISSN 0167-9473 (http://www.sciencedirect.com/science/article/pii/S0167947311003628

Critical fluctuation conductivity in layered superconductors in strong electric field

The paraconductivity, originating from critical superconducting order-parameter fluctuations in the vicinity of the critical temperature in a layered superconductor is calculated in the frame of the self-consistent Hartree approximation, for an arbitrarily strong electric field and zero magnetic field. The paraconductivity diverges less steep towards the critical temperature in the Hartree approximation than in the Gaussian one and it shows a distinctly enhanced variation with the electric field. Our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations in high-temperature superconductors.Comment: 11 pages, 2 figures, to be published in Phys. Rev.

PSD95 and nNOS interaction as a novel molecular target to modulate conditioned fear: relevance to PTSD

Stimulation of N-methyl-D-aspartic acid receptors (NMDARs) and the resulting increase of nitric oxide (NO) production are critical for fear memory formation. Following NMDAR activation, efficient production of NO requires linking the 95 kDa postsynaptic density protein (PSD95), a scaffolding protein to neuronal nitric oxide synthase (nNOS). A variety of previously studied NMDAR antagonists and NOS inhibitors can disrupt fear conditioning, but they also affect many other CNS functions such as motor activity, anxiety, and learning. We hypothesized that disrupting nNOS and PSD95 interaction in the amygdala, a critical site for fear memory formation, will reduce conditioned fear. Our results show that systemic treatment with ZL006, a compound that disrupts PSD95/nNOS binding, attenuates fear memory compared to its inactive isomer ZL007. Co-immunoprecipitation after fear conditioning showed a robust increase in the amygdala PSD95/nNOS binding, which was blocked by systemic pre-administration of ZL006. Treatment of amygdala slices with ZL006 also impaired long-term potentiation (LTP), a cellular signature of synaptic plasticity. Direct intra-amygdala infusion of ZL006 also attenuated conditioned fear. Finally, unlike NMDAR antagonist MK-801, ZL006 does not affect locomotion, social interaction, object recognition memory, and spatial memory. These findings support the hypothesis that disrupting the PSD95/nNOS interaction downstream of NMDARs selectively reduces fear memory, and highlights PSD95/nNOS interaction as a novel target for fear-related disorders, such as posttraumatic stress disorder

Finite temperature Casimir effect of massive fermionic fields in the presence of compact dimensions

We consider the finite temperature Casimir effect of a massive fermionic field confined between two parallel plates, with MIT bag boundary conditions on the plates. The background spacetime is $M^{p+1}\times T^q$ which has $q$ dimensions compactified to a torus. On the compact dimensions, the field is assumed to satisfy periodicity boundary conditions with arbitrary phases. Both the high temperature and the low temperature expansions of the Casimir free energy and the force are derived explicitly. It is found that the Casimir force acting on the plates is always attractive at any temperature regardless of the boundary conditions assumed on the compact torus. The asymptotic limits of the Casimir force in the small plate separation limit are also obtained.Comment: 10 pages, accepted by Phys. Lett.

Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from [email protected], submitted to Phys.Rev.

Charged hydrogenic problem in a magnetic field: Non-commutative translations, unitary transformations, and coherent states

An operator formalism is developed for a description of charged electron-hole complexes in magnetic fields. A novel unitary transformation of the Hamiltonian that allows one to partially separate the center-of-mass and internal motions is proposed. We study the operator algebra that leads to the appearance of new effective particles, electrons and holes with modified interparticle interactions, and their coherent states in magnetic fields. The developed formalism is used for studying a two-dimensional negatively charged magnetoexciton $X^-$. It is shown that Fano-resonances are present in the spectra of internal $X^-$ transitions, indicating the existence of three-particle quasi-bound states embedded in the continuum of higher Landau levels.Comment: 9 pages + 2 figures, accepted in PRB, a couple of typos correcte

Impurity scattering and transport of fractional Quantum Hall edge state

We study the effects of impurity scattering on the low energy edge state dynamic s for a broad class of quantum Hall fluids at filling factor $\nu =n/(np+1)$, for integer $n$ and even integer $p$. When $p$ is positive all $n$ of the edge modes are expected to move in the same direction, whereas for negative $p$ one mode moves in a direction opposite to the other $n-1$ modes. Using a chiral-Luttinger model to describe the edge channels, we show that for an ideal edge when $p$ is negative, a non-quantized and non-universal Hall conductance is predicted. The non-quantized conductance is associated with an absence of equilibration between the $n$ edge channels. To explain the robust experimental Hall quantization, it is thus necessary to incorporate impurity scattering into the model, to allow for edge equilibration. A perturbative analysis reveals that edge impurity scattering is relevant and will modify the low energy edge dynamics. We describe a non-perturbative solution for the random $n-$channel edge, which reveals the existence of a new disorder-dominated phase, characterized by a stable zero temperature renormalization group fixed point. The phase consists of a single propagating charge mode, which gives a quantized Hall conductance, and $n-1$ neutral modes. The neutral modes all propagate at the same speed, and manifest an exact SU(n) symmetry. At finite temperatures the SU(n) symmetry is broken and the neutral modes decay with a finite rate which varies as $T^2$ at low temperatures. Various experimental predictions and implications which follow from the exact solution are described in detail, focusing on tunneling experiments through point contacts.Comment: 19 pages (two column), 5 post script figures appended, 3.0 REVTE

Reverse-Engineering a Transcriptional Enhancer: A Case Study in Drosophila

Abstract Enhancers, or cis-regulatory elements, are the principal determinants of spatiotemporal patterning of gene expression. For reasons of clinical and research utility, it is desirable to build customized enhancers that drive novel gene expression patterns, but currently, we largely rely on “found” genomic elements. Synthetic enhancers, assembled from transcription factor binding sites taken from natural signal-regulated enhancers, generally fail to behave like their wild-type counterparts when placed in transgenic animals, suggesting that important aspects of enhancer function are still unexplored. As a step toward the creation of a truly synthetic regulatory element, we have undertaken an extensive structure–function study of an enhancer of the Drosophila decapentaplegic (dpp) gene that drives expression in the developing visceral mesoderm (VM). Although considerable past efforts have been made to dissect the dppVM enhancer, transgenic experiments presented here indicate that its activity cannot be explained by the known regulators alone. dppVM contains multiple, previously uncharacterized, regulatory sites, some of which exhibit functional redundancy. The results presented here suggest that even the best-studied enhancers must be further dissected before they can be fully understood, and before faithful synthetic elements based on them can be created. Implications for developmental genetics, mathematical modeling, and therapeutic applications are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63213/1/ten.tea.2008.0074.pd

Critical points in edge tunneling between generic FQH states

A general description of weak and strong tunneling fixed points is developed in the chiral-Luttinger-liquid model of quantum Hall edge states. Tunneling fixed points are a subset of `termination' fixed points, which describe boundary conditions on a multicomponent edge. The requirement of unitary time evolution at the boundary gives a nontrivial consistency condition for possible low-energy boundary conditions. The effect of interactions and random hopping on fixed points is studied through a perturbative RG approach which generalizes the Giamarchi-Schulz RG for disordered Luttinger liquids to broken left-right symmetry and multiple modes. The allowed termination points of a multicomponent edge are classified by a B-matrix with rational matrix elements. We apply our approach to a number of examples, such as tunneling between a quantum Hall edge and a superconductor and tunneling between two quantum Hall edges in the presence of interactions. Interactions are shown to induce a continuous renormalization of effective tunneling charge for the integrable case of tunneling between two Laughlin states. The correlation functions of electronlike operators across a junction are found from the B matrix using a simple image-charge description, along with the induced lattice of boundary operators. Many of the results obtained are also relevant to ordinary Luttinger liquids.Comment: 23 pages, 6 figures. Xiao-Gang Wen: http://dao.mit.edu/~we